This invention relates generally to loudspeakers and, more particularly, to planar-type loudspeakers having a substantially flat diaphragm.
Dynamic-type loudspeakers typically include a relatively stiff diaphragm that is coupled to an electromagnetic driver assembly, which basically comprises a voice coil and a permanent magnet. Such loudspeakers are usually mounted so as to occupy an opening in an enclosure or baffle. The interaction of the magnetic field of the permanent magnet and the magnetic field of the voice coil that is produced when a changing current is passed through the voice coil causes the loudspeaker diaphragm to vibrate. Vibration of the diaphragm causes movement of air, which in turn produces sound.
The loudness of the sound produced by a loudspeaker is related to the volume of air moved in front of the loudspeaker by vibration of the diaphragm. Generally, the greater the volume of air moved by the diaphragm as it vibrates, the greater the loudness. The efficiency of the loudspeaker can be measured by the loudness of sound produced relative to the electrical energy provided as an electric current through the voice coil.
For maximum efficiency and sound fidelity, it is known to provide loudspeaker systems with multiple diaphragm/voice coil assemblies. Each diaphragm/voice coil assembly is typically sized and constructed for optimal performance over a specific frequency range. For example, one diaphragm/voice coil assembly may be designed to reproduce low frequencies from about 100 to 500 Hz., while another diaphragm/voice coil assembly might be designed to reproduce high frequencies from about 500 to 20,000 Hz. The combination of all the specific-frequency diaphragm/voice coil assemblies, or drivers, generally produces a more accurate, less distorted sound when compared with systems having a single diaphragm/voice coil assembly to reproduce all of the sound frequencies.
For decades, conventional loudspeaker diaphragms have had a cone-type construction made from pressed paper or the like. In more recent years, certain advances in dynamic loudspeaker design have been provided by the advent of planar diaphragm loudspeakers. Such loudspeakers include a relatively stiff and substantially planar (or flat) diaphragm that is mounted in a frame and that is coupled at its rear surface to the speaker voice coil, such that the voice coil acts like a piston, pressing on the rear surface of the diaphragm and causing sufficient vibration of the diaphragm to efficiently produce sound. Examples of such planar diaphragms are shown and described in U.S. Pat. Nos. 4,003,449 and 4,997,058, both issued in the name of Jose J. Bertagni.
Typically, a planar diaphragm is constructed of a pre-expanded cellular plastic material, such as polystyrene or styrofoam. The frequency response of a planar diaphragm generally is determined by the type and density of its material, and the area, thickness and contour of its sound producing region. Typically, in the design of such a diaphragm, the designer chooses a suitable type and density of material, and then experiments with different sizes and configurations for the diaphragm to achieve an acceptable degree of fidelity in the reproduction of sound in both the low and high frequency ranges.
Some of the advantages provided by planar diaphragm loudspeakers over loudspeakers utilizing conventional cone-type diaphragms include greater dispersion of sound and economy of manufacture. A further advantage is that the front surface of the diaphragm can be molded to take on the appearance of a relatively large acoustic tile, permitting unobtrusive installation of the loudspeaker in ceilings of commercial structures formed of like-appearing acoustic tiles. Alternatively, the diaphragm's front surface can be molded smooth and flat, and a number of such diaphragms can be joined together in a contiguous and seamless array to create a sound screen upon which video images can be projected, as shown and described in U.S. Pat. No. 5,007,707, also issued in the name of Jose J. Bertagni.
One way in which high fidelity sound reproduction has been realized over a wide range of frequencies with unitary, one-piece planar diaphragms has been to form channels in the rear surface of the diaphragm to define different frequency sections having prescribed areas, thicknesses and contours. Each section of the diaphragm is coupled to a different voice coil such that each section and voice coil combination can be used for reproducing a specific range of sound frequencies relatively independently of the other sections of the diaphragm. A rigid frame member in contact with the diaphragm along the boundary between adjacent sound producing regions can be used to isolate them from one another.
Although existing planar diaphragm loudspeakers have been generally satisfactory, there has been need for improvement. One disadvantage of unitary diaphragms is that the density of material selected for them has represented a compromise between the low frequency and the high frequency ranges. Planar diaphragms tend to respond more efficiently to high frequencies when the diaphragms are formed of higher density material; conversely, planar diaphragms tend to respond more efficiently to low frequencies when formed of lower density material. The solution was the choice of an intermediate density material that was deemed adequate, but not optimal for both low and high frequency ranges.
Moreover, it would be a great advantage to install planar diaphragm loudspeakers within building walls of residential structures. The nature of the diaphragm material would then allow it to become a seamless part of the wall surface, so that the loudspeaker could be completely hidden in the wall or ceiling and made totally unobtrusive. Existing techniques, however, have been unable to provide planar diaphragm loudspeakers with satisfactory frequency responses in designs that are small enough to fit within the normal spacing between wall studs or ceiling rafters in conventional residential construction.
Thus, it will be appreciated that there exists a need for improvement in planar diaphragm loudspeakers that will enable better frequency response and efficient reproduction of sound, as well as more compact designs requiring less space for installation and operation. The present invention fulfills these needs.